Ok, with my 2 hour round-trip drives each day, you can imagine that a lot goes through my head. This board tends to get me thinking a lot about what the heck is going on with science and people who don't understand science at all.

So I'll get right to the issue. When the US sent the Pioneer (10, 11) and Voyager (1, 2) crafts, I was amazed. Ok, I'm 26 so I was amazed as the Voyagers were already at the gas giants [img]/phpBB/images/smiles/icon_wink.gif[/img]

Anyway, my parents were amazed when they saw Armstrong set foot on the Moon, on their little b+w TV.

Here's the question.

Which is harder to actually accomplish:

1. Landing a man on the Moon (our closest Solar System neighbour).
2. Successfully navigating multiple probes past the outer planets without any of them being completely destroyed by the unknown.

I'd be interested in knowing what you guys and gals have to say about this, as I'm leaning towards #2, initially. I just feel that going to the Moon is an amazing thing but being how close it is to us (and I realize the Moon landing plans had to take into account the variable called "humans" as opposed to Voyager 2's unmanned race to Neptune), isn't the feat of sending these probes as far as they have gone without any terrible problems more of a feat?

I know the story. "US faked the landings to scare the Russians." Scare them into what, seeing how far away the US could GET from Russia? hehe. Think about what the Russians may have thought, "Oh boy, the US has landed on the moon and we have not. The further away they are from us, the better!"

That's of course just a satirical way of looking at it.

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The US and the USSR had probes zooming about the Solar system ever since Sputnik was launched. Probes are much simpler to build. I think that most, fairly modern, ones just run off of a cesium brick, no need for shielding to protect the frail humans. You should be able to find a list of probes, where they went, etc. on the net somewhere. If not I will find one when I get home. -Colt

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"I think that most, fairly modern, ones just run off of a cesium brick, no need for shielding to protect the frail humans."

What do you mean by a "caesium brick"? Are you talking about an RTG? If so, I think it's plutonium.

Number 1 requires extra provisions, such as life support and the return ticket. That makes it more expensive and cumbersome, but in terms of technological ability, it is actually easier than number 2.

In number 2, you have no real time control because of the vast distance and the tricky orbital mechanics and increased duration of mission make it much harder.

Jay has a good article on this:
http://www.clavius.org/techmars.html

That's what I was mainly thinking about - the actual level of difficulty. Right now I think they are still trying to wake up Galileo (the probe, not the dead guy), which is of course a more recent probe. The first probes sent out by the US to the outer planets is what I'm referring to, of course, when talking about probes. Sure, Russia and the US have both had probes to Venus, the Moon, and Mars. "That's easy!" lol

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"Don't worry, everything is getting nicely out of control." -Douglas Adams

That's a big question. And really it's an apples and oranges question.

Manned space flight and unmanned space flight have very different design criteria. Humans are very fragile creatures and cannot stand much variation in temperature and pressure. And a vast amount of equipment must be provided to cater to their biological needs, that doesn't directly contribute to a mission. And equipment for manned space flight must be engineered to much higher degrees of quality and reliability. So a manned spacecraft is probably two orders of magnitude more difficult to build than an unmanned spacecraft. And consequently it is about two orders of magnitude more expensive.

On the other hand, it's very hard to duplicate the advantage of a skilled human pilot. The lunar module, for example, was an excellent flying machine, but its success lay in the skill and judgment of its human pilot. Apollo 11 would have crashed and burned had Neil Armstrong not taken quick, adaptive action to avoid an unsuitable landing site. This advantage also extends to repairs. You just can't cram that much smarts into a computer pilot, and distance prevents suitable remote control.

Your chances of mission success rise dramatically when skilled humans are as directly in control as possible. But human observation and adaptive exploration are also important. There is no substitute for direct, educated, skilled human observation. On-site investigation is the most effective by far.

The problem of going to the moon versus going to distant planets bears scrutiny. We understand a lot about how to navigate in the earth-moon system. Voyage times are short, and communication latency is manageable. The problem of going to the moon, from a pure celestial navigation standpoint, is not that heinous.

Sending things out into the solar system requires a more general understanding of the gravitational problems of the solar system, and those are non-trivial. I just attended a technical meeting on the GRAPE-6 system, a special purpose computer used to perform computational simulations of n-body gravitation for objects in the Kuiper Belt. This is the kind of muscle that has to be brought to bear in order to understand how to send things out there safely and reliably.

Communication latency and the unknowns of the outer solar system means the spacecraft faces more unknowns than close to home. The voyages are more dangerous and less sure in an astrodynamical sense.

One comment: you don't really *need* huge computing power to successfully send a probe to the edge of the solar system. You make the point on your webpage that just because we use such technology to solve a problem today does not mean the problem was impossible to solve before the technology existed. If we were forced to tackle the problem without high-powered computers, we could make our best guess based on a simpler analysis (something like the patched conic method in orbital mechanics, which breaks the trajectory up into several 2-body problems), then when the probe is en route we can closely observe its trajectory and make the small adjustments needed to hit right on the money. This may not be the most efficient way to do it, but since the timeframe is so large for such a long journey I think it would definitely work.

I'm not sure of all the details on how they got the Pioneer, Voyager, and Galileo probes to their proper destinations, but clearly the kind of computing power you are referring to did not exist when those projects started. So there *must* be a way to do it without all the fancy computers...it just wasn't as efficient and there probably was slightly more risk involved (or slightly lower odds of success). Emphasis though on *slightly*, I think.

One comment: you don't really *need* huge computing power to successfully send a probe to the edge of the solar system.

I know, I just wanted to mention GRAPE-6. [img]/phpBB/images/smiles/icon_smile.gif[/img]

There are problems in long-period orbits that are of special concern computationally, and navigationally, but the same methods will work for deep-space navigation as work for close-in navigation. It's simply a matter of good initial guesses.

We can provide a moon-bound spacecraft with a very accurate picture of its own dynamics. The flight control system has little correction to do. With greater unknowns (such as those that arise from observing long-period orbits) we have to rely on the spacecraft's ability to dynamically adapt. That means more fuel, better flight software, etc. Those are still expensive things, so it makes sense to expend a lot of supercomputer cycles on the ground trying to build a more accurate pictures of the situation.

I'm not sure of all the details on how they got the Pioneer, Voyager, and Galileo probes to their proper destinations

They didn't. Those spacecraft simply had looser constraints and lower expectations than what we're planning for the future. It's no longer sufficient simply to get a spacecraft to the Jovian region. We want to park the thing in a very precise point in space and time.

Space exploration lives constantly at the bleeding edge.

And to be fair, you don't need to know anything about planetisimals in the Kuiper belt in order to get a spacecraft to Jupiter. GRAPE-6 isn't necessary for that. It's only necessary if you need to understand and model the behavior of these objects.

It's not clear in the original question whether we're talking about Apollo-era technology, or the state of the problem in general. We demand more from modern missions than we did from the early probes.

I would definitely go with #1 because of what it took:

Lunar module - Unique space vehicle
Command module - At least as complex as any unmanned probe
Saturn V - Arguably the most amazing machine ever built.

Just for starters.

Admittedly, the calculations to get a vehicle to the outer planets are complex. (I used to work with a guy whose full-time job it was to calculate how to get a mission into a particular sort of solar orbit using lunar flybys and a minimum of fuel - he had to do this separately for each date on which it was possible for the mission to launch.) But there's not that much "unknown" in the outer solar system, at least not deadly. Even things like Jupiter's radiation belts were known and anticipated for missions like Galileo. Such missions are quite an accomplishment, but I think they pale before the Apollo missions.

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<font size=-1>[ This Message was edited by: ToSeek on 2002-11-22 21:36 ]</font>

There's one aspect of the Apollo missions I neglected to consider: rendezvous. It's harder than you think, and that greatly complicates the Apollo mission profile.

The Apollo hardware has a certain elegance. I concur: the Apollo command module was a quantum leap ahead of Gemini. The Saturn V was the most admirable launch vehicle ever devised. And in my opinion, the lunar module is the most pure, most perfect, most well-suited flying machine yet devised by humankind.

I regret ever mentionning Galileo, seeing as it's nowhere near the same timeline as Apollo and the first outer-planetary probes.. In my opinion Galileo was probably far easier given the learned knowledge of past missions. I bet if they were to do another Moon walk soon, it would be far easier to figure out and do compared with back then, based on the materials and given knowledge from the past.

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"Don't worry, everything is getting nicely out of control." -Douglas Adams

Now... if NASA could just come up with a way to shorten that two-hour commute....

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